In filling level measuring by means of transit time methods, an echo profile, an echo function or an echo curve is generated cyclically in order to, from this, in an evaluation algorithm that is also referred to as “useful-echo identification”, identify the “correct” echo that emanates from a feed material surface in order to subsequently, in a further algorithm that can be referred to as “echo measuring”, measure the transit time of this echo. Transit time sensors that are used for such filling level measuring may process the tasks of echo evaluation and echo measuring completely and in mutual alternation, as a result of which a rigid serial sequence may arise. Evaluating an echo may involve the determination of the reflection from the feed material surface by means of an echo profile of the entire measuring span, and measuring may involve determining a distance value and/or a filling level value of the echo profile of the filling material reflection.
From DE 10 2006 006 572 A1 it may be known that by sampling relatively few values of an IF-signal an envelope and also phase angles of the IF-signal are to be computed in each case from only two sampling points.
DE 199 25 216 C1 may disclose reference measuring of unwanted signals and subtracting a component of a frequency spectrum that is caused by interference frequencies from a sampled measuring signal to a differential signal.
Furthermore, in DE 44 07 369, determining a correction value from a fraction of a carrier frequency, which fraction has been determined by the phase angle, may be described.
U.S. Pat. No. 5,457,990 may disclose a method for registering a liquid level in a tank by means of an analysis window.
Furthermore, U.S. Pat. No. 5,207,101 may describe the periodic supply of energy to a transducer in order to transmit energy pulses that are reflected by the surface of a material to be measured.
In EP 1 562 051 A2 a pulse measuring process may be described which during a first phase generates an echo profile, and which interrupts the first phase in order to charge an energy storage device at least once.
DE 43 27 333 A1 may describe a method for measuring the filling level of a liquid in a container according to the radar principle, wherein unwanted signals that occur in a measuring spectrum and that are independent of the filling level height of the liquid are corrected by means of the measured intensity of a first unwanted signal.
EP 1 225 455 A2 may describe the subtraction of undesired radio frequency interference.
Furthermore, U.S. Pat. No. 6,972,712 B1 may disclose the storage of a pulse shape in a ROM during pre-installation calibration.
DE 31 074 44 may describe a method for a high-resolution pulse radar.